A fixed support of voice coil motor is a base for winding coil thereon. One conventional fixed support is shaped like a plate, from which several pins extrude for receiving winded coil. For a better rigidity, the plate of fixed support is usually machined in a relatively great thickness. However a fixed support with thick plate will reduce the density of magnetic flux through the plate, which is generated by pairs of permanent magnets at each side of the plate, thereby lowering output power of the voice coil motor adopting the fixed support. Even if the thickness of the plate was simply thinned out, the rigidity of the plate would be degraded, thus making this change unlikely. Another fixed support is formed together with coil by an injection mold. Through the fixed support could be machined much thinner than the forgoing one, it suffers financial burden due to the high cost of the injection mold. In many cases, when cost turns to a crucial issue, the fixed support manufactured by injection mold will not be a cost efficient one anymore. Thus, there is a huge need to provide a fixed support with a plate as thin as possible, while maintaining its cost competitiveness.
FIG. 1 shows a conventional fixed support of voice coil motor, which includes a plate 30, several pins 10 extruding from the plate 30, and coil 20 winded around the pins 10. As a result of the wide thickness of the plate 30 of fixed support, the magnetic flux density, which is generated by pairs of permanent magnets from each side of the plate 30, is relatively low, therefore, reducing output torque of the voice coil motor adopting the fixed support. Moreover, as the mass distribution along the transverse direction of plate 30 remains asymmetric, the fixed support would likely vibrate fiercely when the voice coil motor rotates.
FIG. 2 shows another conventional design for fixed support 40 of voice coil motor. The fixed support 40 is fabricated much thinner than the above mentioned one through an injection mold. The Coil 50 is winded inner the fixed support 40, so as to ensure the fixed support to remain in a thin thickness and a relatively balanced mass distribution. Although the fixed support 40 provides better performance for voice coil motor than the above one does, its exists several shortcomings. Owing to the high cost of injection mold and complication of winding coils for various shaped fixed supports, the fixed support 50 will hard to be cost efficient unless manufacturing it in mass production.